This research project aims to demonstrate diagnostic ability of high frequency electrocardiogram (HF-ECG) beyond the capability of conventional ECG in myocardial infarction (MI). The empasis will be to test the possibility of using the HF-ECG to improve diagnosis of MI in the presence of ventricular conduction defects and to determine whether HF-ECG's contain prognostic information with respect to ventricular arrhythmias. The HF-ECG's will be recorded in animals with acute or chronic MI and later analyzed by computer for quantitative evaluation of HF components in the QRS comples. The electrophysiologic mechanisms of HF components and their relationship to the incidence of ventricular arrhythmias will also be studied in these animals. The results of this project may lead to improved methods of diagnosis of MI and identification of patients with high risk for fatal arrhythmias. In a related project, the effects of new antiarrhythmic agents will be studied using diseased tissue preparations. Microelectrode studies will be carried out on infarcted tissues excised from the hearts of animals following MI. This will allow us to study the electrophysiologic mechanisms of ventricular arrhythmias and the modes of action of new antiarrthymic agents under conditions which mimic the changes encountered in clinical MI. The changes in excitability of the ischemic bundle branches will also be investigated in vivo, and the changes will be correlated with the occurrence of bundle branch block and re-entrant ventricular arrhythmias. These studies will improve our understanding of ventricular arrhythmias and decreased fatality of patients with MI.